Gas density meter



' oct. 11, 1949. CRINER r 2,484,207

GAS DENSIQTY MEIER Filed Feb. 16, 1945 2 Shee'ts-Sheet 1 ATTORNEYPatented Oct. 11, 1949 UNITED STATES PATENT OFFICE GAS DENSITY METERApplication February 16, 1945, Serial No. 578,330

Claims.

Our invention relates to a novel type of densitymeter which is of theremote-indicating type, giving a direct reading of the density of a gas,automatically corrected or compensated for both pressure andtemperature. It was primarily designed for measuring thehydrogen-concentration in the hydrogen-air mixtures of hydrogen-cooledturbogenerators, but its general principles are susceptible of measuringthe purity of any gas, or, in general, of measuring the density of anygas, whatever its temperature or pressure, compensated for any standardtemperature and pressure.

An object of our invention is to utilize a blowerdevice for producing agaseous pressure which is a function of the gas-density, the absolutepressure and the absolute temperature of the gas to be measured, and toutilize a frictionless piston, operating against a spring, fortranslating that pressure into displacement, and to utilize areluctance-gauge and a suitably calibrated milliammeter to translatethat displacement into electric currents and meter-responses or otherourrent-indications or responses. A reluctant-gauge is aWheatstone-bridge measuring-instrument, two legs of which consist ofcoils which are disposed on two opposite E-shaped cores having a movablearmature between them. The movable armature moves toward one core as itmoves away from the other, thus detecting small movements ordisplacements of the core by converting such displacements intodifferences between the reluctances of the magnetic paths of the twocoils of the Wheatstone bridge. The milliammeter, in this case, can becalibrated directly in percentages of hydrogen-purity, or percentages inthe gaspurity of whatever gas the meter is to be calibrated for, or itmay be calibrated in any other units of gas-density.

In the preferred form of embodiment of our invention, thedensity-measuring instrument of the type just described is compensatedfor the absolute pressure of the gas and the absolute temperature of thegas, by utilizing a linkage for applying the piston-displacement to themovable armature of the reluctance-gauge in such a manner that thelength of one leg of the linkage is responsive to temperature andpressure in a manner which is inverse with respect to the response ofthe blower-pressure to temperature and pressure. A suitable form of suchcompensating link is provided by a bellows, containing a fixed quantityof gas, and having a displaceable end, the displacement of which ilinearly responsive to the volume of the gas entrapped in the bellows,and hence directly responsive to the absolute temperature and inverselyresponsive to the pressure of the ambient gaseous medium in which thebellows is located, If such a bellows is placed within the gas to bemeasured, the volume of the gas within the bellows is responsive to thequotient of the absolute temperature divided by the absolute pressure orthe gas to be measured, because that temperature and that pressure arecommunicated from the gas to be measured to the gas within the bellows.

A further object of our invention is to provide a density-meter of theclass described, with facilities and arrangements for convenientlycalibrating the same in air, so that it can be utilized in hydrogen orin gases of density other than that of air.

A preferred form of embodiment of our invention is illustrated in theaccompanying drawing, wherein Figure 1 is a somewhat diagrammaticcrosssectional view of apparatus embodying our invention,

Fig. 2 is a detail cross-sectional view of the compensating bellows, onthe section-plane indicated by the line II-II in Fig. 1.

Fig. 3 is a sectional view of the reluctance gauge, as would be seen bybreaking away some of the parts from Fig. 1, with the coils of thereluctance-gauge indicated diagrammatically. The section-plane of Fig. 3is indicated at III-III in Fig. 4.

Fig. 4 is a diagrammatic sectional view of the reluctance-gauge, on theplane indicated at IVIV in Fi 3.

Referring to Figure 1, the gas to be measured is contained in agas-filled vessel 5, which may be the casing of a hydrogen-cooledgenerator (not shown), or the smoke-stack of a furnace (not shown), orany other gas-filled space for which it is desired to determine thepercentage of the volume of the hydrogen-content to the volume of themixture of hydrogen and air, as in the case of a hydrogen-cooledgenerator; or to determine the percentage of the carbon-dioxide contentof flue gases; or, in general, to determine the relative density of anygas, preferably automatically compensated for temperature and pressure.

Our density-gauge comprises a suitable type of gas-pressure gauge, whichis illustrated as comprising an enclosed gas-tight chamber 6, whichreceives gas from the gas-chamber 5 under test, through a pipe or othergas-opening or connection I, and preferably also through a reducediloworifice 8, which can be chosen to limit the spring l4.

velocity of gas-flow in a manner which will subsequently be described.

One end of our gas-gauge chamber 6 is partitioned oif by a piston 9, theedges of which are sealed with a flexible bellows-like sealing-memberll, so that no gas can pass from one side of the piston to theotherrwithin the chamber 6. Vie use the term piston to refer to anymovable pressure-responsive gauge-element, rigid or nonrigid. In ourillustrated form of embodiment of our invention, we have shown thepiston 9 as a rigid disk-like member, carrying a rigid pistonarm l 2,preferably not centrally disposed but disposed near one edge of thepiston '9, and extending back from it for a considerable distance, at

right angles to the piston, said arm !2 being contained altogetherwithin thecasing 6,

The piston-arm I2 is mounted to have a small amount of substantiallyrectilinear motion by means of a parallel linkage l3 and M. The

front link I3, or the link closest to the piston 9,

is pivoted at l5 to the piston-arm I2, at the top 'of the link l3, whilethe bottom of the link I3 is pivotally supported at I6 on the bottom ofthe housing 6. The pivotal supports l5 and 16 are preferablyfrictionless pivots of a known kind,

and the pivot-representations in the drawing are intended only as adiagrammatic representation of any suitable pivots.

The rear link M of the parallel linkage [3-44 which supports thepiston-arm i2 is in the form of one or more leaf-springs M, the top ofwhich is clamped, at I1, to the piston-arm 12, while the bottom of thepiston-spring i4 is clamped, at l8, to the bottom of the housing 6. Thepistonspring I4 is biased to press the piston 9 forwardly, 'or away fromthe spring, until the spring l4 moves up into contact with a fixed armor shelf I9 extending up from the bottom of the housing 6.

The gas is drawn out of the chamber or housing 6 through an outlet 2|,which is suitably connected, as by piping 22, to the inlet end 23 of acentrifugal blower 24, which is driven by a constant-speed motor 25,preferably in the form of a synchronous polyphase motor. Thebloweroutlet 26 is suitably connected, as by piping 21, to ahigh-pressure inlet 28 on the piston side of the chamber 6, so that thepressure-difference between the high-pressure side 26 and thelowpressure side 23 of the blower is impressed on opposite sides of thepiston 9, so as to press the piston backwardly against the restraint ofits The high-pressure outlet 25 of the blower is also connected, througha T-connection 29 and a pipe 30, to an inlet-opening 3! in thegas-chamber 5 containing the gas to be sampled.

In this manner, the blower 24 continuously draws air through the pipe 1,and through the density-gauge chamber 6, and returns it back to theoriginal gas-container 5, impressing, across the piston 9 of the gauge,whatever pressuredifference is produced by the rotation of the blower 24in the sampled gas. The restricted inlet-opening 8 is preferablyadjusted so that only a relatively small quantity of gas is permitted topass, thegas-fiow being throttled down so that the blower 24 operates onthe upper or constant portion of its pressure-volume curve, so

that the diiferential pressure produced by the blower is independent ofthe rate of gas-flow through the blower.

V The displacement of the piston 9, as a result of thepressure-difierence operating against the restraint of the spring I4, isapplied, by a suitable linkage, subsequently described, to areluctance-gauge 33, which is shown more in detail in Figs. 3 and 4. Thereluctance-gauge consists essentially of two oppositely disposedE-shaped laminated cores 34 and 35, separated by a large airgap which isnearly filled with a movable laminated armature 35. The two E-shapedcores 34 and '35 are mounted upon a base-plateor plates the two springs'32 and 33 serve as a parallel linkage for permitting the front-plate3i, and hence the armature 3b, to have a substantially frictionlessrectilinear motion, so that the armature 36 may approach toward the oneor the other of the two E-shaped cores 34 and 35.

We show a double reduction-linkage for transferring the piston-movementar to the reluctance-gauge 33, to produce the gauge-movement of thegauge-armature 33. In the particular form of linkage which we haveshown, the front link [3, which supports the piston-arm i2, is providedwith an intermediate pivot-point 45 which has a motion b/a times themotion of the motion 30 of the piston 9, where b is the length of .theshort arm l6--t5, while a is the length of the long arm l6l5, or thetotal length of the link l3. 7

The pivot-point 45 is connected, by means of a link 45, to a secondpivot-point 31 which is carried by the bottom of a second linkage-member48. The linkage-member 68 has a short bottom piece 39, and a rigidupstanding portion 5! which is pivoted, near its top, at 52, to a boss53 carried 7 51 for an adjustable connection 58 with the top end of alinkage or rigid portion 59 of the second linkage 48. The bottom end ofthe member 59 is pivoted or otherwise connected to the bottom portion 69of the linkage d8, by a connection which is shown at 6! The constructionof the bellows 55 is indicated schematically in Fig. 2. The essentialfeatures of the bellows-design is that it has a stiff flat base orrear-plate 52, a stifi flat front-plate 63, and flexible bellows-likeside-walls 64, so arranged that the separation between the two plates 62and 63, as the fixed quantity of gas which is entrapped in the bellowsexpands and contracts under differences of temperature and pressure,will be exactly proportional to the volume of the entrapped gas. andhence proportional to the quotient of its absolute temperature dividedby its pressure.

'As shown in Fig. 1, the forwardly extending arm 56 of the bellows 55provides, in effect, a rigid bell-crank arm Z, of adjustable length, theZ being the distance between the vertical plane 65 passing through thefixed pivot 52 of the linkage-member 5i, and the vertical plane 36 of avertical link 61, the top end of which is secured, at 68, to the top ofthe member 59, and thence to the arm 56, while the bottom of the linkage51 is connected to a block 69 carried by the armature-plate 4! of thereluctance-gauge 33. The length of the longbell-crank arm 5| is thevertical distance between the fixed pivot 52 at the top and thelinkage-pivot 41 at the bottom, so that this arm 524'I constitutes thelong arm of a bell crank, having a length 0, while the distance I of thebellows-arm 56 constitutes the short arm of the bell crank. The shortbell-crank arm I is of a length determined by the separation between thefront and back plates 62 and 63 of the bellows 55, and this distance Iis such that it would be zero at the absolute zero of temperature or atinfinite pressure, or when the bellows 55 is totally collapsed.

From the linkage a, b and the bell-crank e, Z, it is easy to express therelationship between the gauge-displacement m and thepiston-displacement w as shown by the formula:

The piston-displacement w is directly proportional to thepressure-difference which is produced by the blower 24, and thispressure-difference of the blower is inversely proportional to theabsolute temperature T of the gas, and directly proportional to theabsolute gas-pressure P and a function of the gas-density or of thegas-purity, which we may write f(Vh/vm), where Vh and Vm arerespectively the volume of the hydrogen-content of the mixture and thetotal volume of the mixture of the hydrogen and air which is containedin the hydrogen-filled vessel 5. The piston-displacement 1: may thus bewritten:

a jg; 2)

Equation 4 shows that the displacement m or the amount of upward ordownward movement of the armature 36 of the reluctance-gauge 33, islinearly responsive to the same function of the gas-purity ratio Vh/Vmto which the blower 24 responds, in building up its blower-pressure orgas-pressure-diiference. If the blower 24 is of the centrifugal type,with the gas-flow throttled as at 8, the pressure-difference created bythe blower 24 is of the type expressed by a constant times )(Vh/Vm)where where in and k2 are constants. This is a straight-line response.

The gauge-displacement x represents the distance by which the length ofthe airgap II is reduced, between the armature 36 and the top E-shapedcore 34, and the distance by which the airgap 12 is increased, betweenthe armature 36 and the bottom E-shaped core 35 of the reluctance-gauge33. Since the airgap 1| or 12, as the case may be, representssubstantially the entire reluctance of the respective flux-pathsincluding means for adjusting the effective length l.

the cores 34 and 35, respectively, this means that the two reluctancesare varied in opposite directions, one increased and the otherdecreased, in linear response to the gas-purity-ratio Vh/Vm.

The changes in the reluctances of the magnetic flux-paths of the upperand lower magnet-cores 34 and 35 is measured by two coils l4 and 15,respectively mounted on the central legs of the two E-shaped cores 34and 35. These two coils l4 and 15 are connected as two legs of aWheatstone bridge, the other two legs of which consist of an inductance16 having a variable or adjustable mid-tap 11. This Wheatstone bridgemay be traced from a conductor 18 to the coil 14, a conductor 19, thecoil 15, a conductor 80, the tapped inductance I6, and back to theconductor 18.

Constant-voltage alternating current is supplied to the conductors l8and of the bridge from a single-phase line 8!, through avoltageregulator 82 which holds the voltage constant, and a variabletransformer 82, which can be utilized for meter-reading adjustments, aswill be subsequently described. The current produced by any unbalance ofthe respective arms of the bridge is measured by a milliammeter 83,connected between the mid-tap T! and the conductor 19. Since thereluctance-variation of the magnetic paths of the coils 14 and 15 isresponsive to the gas-purity-ratio Vh/Vm, the milliammeter-scale 85 maybe calibrated directly in the percentage of hydrogen-content in themixture of hydrogen and oxygen, as shown by the lower scale, or it maybe calibrated in gas-density in any scale that may be desired.

In operation, the compensating bellows 55 compensates for thegas-pressure P and the gastemperature T. In order that this compensationmay be perfect, (or substantially perfect), it is necessary that thelength Z of the short bellcrank-arm shall be properly chosen, as byloosening the attachment-screw 58 and sliding the same in the slot 51 inthe bellows-arm 56, and then re-tightening the screw 58, this beingintended as symbolic of any suitable adjustment- This adjustment shouldbe such that a change in the gas-pressure P does not cause any variationin the meter-indication, within the operating-range of the instrument.This adjustment will usually be made at the factory, or, ifmanufacturing-tolerances are adequately controlled, the distance I maybe predetermined without the need for adjustment.

The zero-reading 86 of the instrument may be adjusted by stopping theblower-motor 25, and adjusting the mid-tap 'l'l until the meter 83 readsOn the particular meter 83 shown in Fig. 1, the lower meter-scale iscalibrated in percentage of hydrogen-content of a mixture of hydrogenand air. The first mark after zero is for pure hydrogen, or hydrogen,then 90, then 80, and finall 70% hydrogen, which is as far as the meterneeds to go, as the mixture becomes explosive after that.

For convenience in the making of calibrationadjustments by the user ofthe instrument, the meter-scale 85, as shown in Fig. 1, is provided withan upper scale, having tWo marks on it, in the top half of the scale 85.One upper mark is for pure carbon dioxide, as indicated at CO2, and theother is for air, as indicated by AIR. The CO2 marking is so chosen thatit is coincident with the 70% hydrogen mark, although any other CO2scale could have been chosen. Then the AIR;

7; w-T be at sameintermed ate point. as indecatieda.

Inorder that: the meter 8% may: have: two scales; an, upper scale: forither air or carbon dioxide-L nd a lower scale for y o e We;provide'means for changing the spring-constant of the piston-spring UL,We have shown this very diagrammatically in, the form, of a stop-screwcc li'ig. 1'), which: may be set up: so as to engage the pistonvspring-M thus changing the eflective length, or the springand hence thespring-setso; that it will exert a. stronger spring-force for resistingthe greater gas-pressures produced the pump 24 is. operating in eitherair or carbon dioxide, When the pump is operating in hydrogen, or inhydrogen-air mixtures of 70% ta 1 90% hydrogen, the stoprscrew 90- isscrewed back until it clears, the pistornspring id at all times;

The, vertical height. or the exact position of the tap for theyset-screw 9,9. is adjusted (or predetermined) at the factory, so: that,if the variable transformer 82' is ad-jnstedgso, that the meter 83reads, exactly at; the mark AIR when the instrument is operating in:air, and with. the stop-screw .0, set, up, the' instrument will becorrectly calibrated for hydrogen and hydrogeneair mixtures with the.step-Shrew setback out of possible contact, with the piston-spring M.01' the adjustment may be made, with carbom-dioxide instead oi; air,,using the. (3,0,2 mark and, the same set-up position oi he, stop-screw9h.

Q the; correct,- calibration may be assured by so adjusting thetransformer 82, or the voltager g lator 82 as, to. maintain a p escribedfill-cyole. voltage, across. the. conductors l8. and as.

Qur inyention, provides. a means for obtaining a a as-density indicationat a, remote point. Ifhe a means for subjecting the piston toages-pressure developed by a blower 24; operating in the gas to bemeasured, provides a means for converti-ng Variable gas-pressures, intovariable electric currents, which can readily be measured at a,distance.

Our addition of the compensating-bellows 55 provides a means forautomatically compensating for, or eliminating the response to, eitherthe gas-pressure or the temperature of the test-gas, so that a directindication may be had of the composition or density of the, gas, or itspercentage of purity if it is mixed with a diluting or contaminatinggas.

While we have somewhat diagrammatically indicated our; invention in asinglev preferred form of embodiment, we are not limited to the preciseform, or to all of the features shown. The invention may also be usedwith other features or with, refinements which are not shown; We desire,therefore, that the appended claims shall be accorded the broadestconstruction consistent with. their language.

We claim as our invention:

1. An instrument for responding to a densitycharacteristic of a gas,comprising means for providing a chamber containing the gas to beresponded to, pressureecreating means, in communication with said,chamber, ior creating a pres sureadifiierence is responsive to; adensitycnaracteristic of the gas in. question, displacement-produoing:meanswhich is responsive to said pressure-dinerencei movable-element;displacement-responsive means for obtainin the desired response to thedesi d; densityharac teristic of the gas. in question, and conn ctingmeans, including avariable-length, arm or cans;- ing thedisp1acem6ntrreSp0'rIS means.- to be we tuatedi in response; to thedisplacement produced by said displacement-Produc means. said var--iable-length arm comprising an expansible and contractable hollowgas-tight means disposed within said chamber and constituting agas-responsive adjustment-device which is, inversely re; sponsive toonly a part of; the density-characteristic to which thepressure-creating means responds.

2. An instrument for responding to the density of'a, gas,comprising-:meansvfor providing a chamber containing the gas to beresponded to, a moirable-element pressure-gauge including a moi/7- ableboundary-wall of" said chamber for providing a displacementv which isresponsive to the pressure-diflerence on. opposite sides of said morableboundary-wall, amoyable-element displace,- ment-responsive device.disposed within said chamber; movementcommunicating. means, within said,chamber, constituting a variable,- length arm, for communicating thepressuregange displacement of said movable boundarywall to the.displacementeresnonsive device, sai movement-communicating meansincluding a gas-filled, gas-tight, hermetically sealed expansible andcontractable hollow body disposed within said chamber for controllingthe length or? said arm, said hollow body containing a fixed quantity ofentrapped gas which is thus subjected to the temperature and thepressure of the gas to be responded to, anda blower-means having aninlet in communication with said chamber and having an outlet incommunication with a space outside of said movable boundary-wall: orsaid pressure-gauge, thus creating the pressure-dineronce which is.efiective on, opposite sides of the pressurergauge.

3. An instrument for responding to the density of a gas, comprisingmeans for providin a chamber containing the gas to be responded to, amovable-element pressure-gauge including a movable bounda-ry-walt ofsaid chamber for providing a displacement which is responsive tothepressure-d-ifierence on opposite sides of said movableboundary-wall,v a. movable-element displacementresponsive devicedisposed within said chamber; movement-communicating means, constitutinga variable-length arm, within said chamber, for communicating thepressure-gauge displacement of said movable boundary-wall to thedisplace merit-responsive; device, said movement-conundnicating meansincluding a. barometric means which is disposed within said chamber andwhich responds directly ta the, absolute temperature of the gas to beresponded to, and indirectly to the absolute pressure of. said, gas,said barometric means being operative to control the effective length ofsaid arm, and a blower-means having an inlet in communication with saidchamber and having an outlet in communication with a space outside ofsaid moyable boundary-wall of said pressure-gauge, thus creating; thepressure,- di-fference which is effective on opposite sides ofthepressurergauga V 4., An. instrument tor measurin the density or a.testrsasgwithi automatic compensatio for both the gas-pressure and thetemperature of the test-gas, comprising a movable-elementdisplacement-responsive meter, calibrated in terms of the gas-density tobe measured, a movable element pressure-responsive means for prodv adisplacement Which is responsive to a difference in gaseous pressures,movement-communicating means for causing the displacement of said meterto be responsive to the displacement of said pressure-responsive means,said movement-communicating means comprising a gasresponsiveadjustment-device for causing the rm tio of the meter-displacement andthe pressureresponsive displacement to vary directly in response to theabsolute temperature of the testgas and inversely in response to theabsolute pressure of the test-gas, substantially independently of thedensity of the test-gas, pressure-creating means for creating apressure-difference which is responsive to a density-characteristic ofthe test-gas and which is directly responsive to the absolute pressureof the test-gas and inversely responsive to the absolute temperature ofthe test-gas, and gas-pressure-communicating means for causing thediiference in gaseous pressures in said pressure-responsive means to beresponsive to the pressure-difference created by said pressure-creatingmeans.

5. The invention as defined in claim 4, characterized by said meterhaving a second ca1ibration in terms of the gas-density of some knowngas, adjustment means for adjusting the setting 10 of themeter-readings, and scale-changing means for making a predeterminedchange in the response of said pressure-responsive means to thedensity-characteristic of the test-gas, whereby the metcr readings forboth scales are correlated.

HARRY E. CRINER. RENEA. BAUDRY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,725,554 Winton Aug. 20, 19292,000,308 Von Schutz May 7, 1935 2,027,875 Odendhal Jan. 14, 19362,042,374 Wunsch May 26, 1935 2,082,539 Fisher June 1, 1937 2,197,370Sullivan Apr. 16, 1940 2,211,627 Morgan et a1. Aug. 13, 1940 2,223,705Roudnicky Dec. 3, 1940 2,260,837 Kuehni Oct. 28, 1941 2,285,045 PfeifferDec. 2, 1941 2,318,153 Gilson May 4, 1943 2,404,993 Sullivan July 30,1946 FOREIGN PATENTS Number Country Date 15,787 Great Britain 1912120,440 Great Britain Nov. 7, 1917 57,963 Norwa May 10, 1937

